The present invention relates to a method for sintering a mixture of oxidized titanium powder and an active metallic component, and to a product produced by the method.
Sintered products made by calcining the powdery mixture of oxidized titanium and metallic oxides have been utilized as a catalyst or adsorbing agent for effectively removing harmful materials from exhaust gases.
In a number of cases a dry type treatment using a catalyst or adsorbing agent has been employed for treating the gases containing harmful materials, for example, various kinds of exhaust combustion gases containing the nitrogen oxides like NO and NO.sub.2 (described by NOx below) and the sulfur oxides (described by SOx below), exhaust gases from nitric acid plants, exhaust gases from iron producing plants, Claus tear gases containing many kinds of bad smelling materials like hydrogen sulfide, exhaust gases from paper manufacturing plants and other kinds of exhaust gases, because the treatment makes a process simpler and does not discharge a secondary waste.
When the dry type treatment is practiced, a static-bed reactor is generally employed by packing at random a catalyst or adsorbing agent in a shape of columnar, cylindrical, ringed, sherical or granular pellets. In these cases, a large amount of exhaust gases to be treated necessarily has required a larger size for a reactor packing the catalyst or adsorbing agent. Under such a condition, the catalyst or adsorbing agent is liable to be [given a] damaged by compression due to their own weight. Thus, sufficiently high mechanical strength has been required for the catalyst or adsorbing agent itself.
Many solid and misty materials are contained in the exhaust gases along with the harmful materials. For example, the exhaust combustion gas due to the chemical fuel such as coal, heavy petroleum and crude petroleum contains non-combustion materials like the oil smoke, an exhaust gas from a coke oven or a sintering oven contains a large amount of dust like heavy metals and ashes, and an exhaust gas from a glass dissolving furnace or a paper manufacturing plant contains a strong viscous mirabilite or alkali fume.
When such gases are fed to a static-bed reactor with the pellets, the deposits, e.g. the dust, increases a pressure loss in the reactor with the passage of time to deflect the flow of gas and to close the reactor in the worst case.
Thus, it can be provided to employ a process using a parallel flow type reactor, which is constructed to be small in pressure loss and small in size, with a catalyst of a honeycomb structure or plate structure having a base made from a metallic plate or wire net. However, there exists a technical problem on the shaping property and mechanical strength, when sintered products which can be used in either of the static-bed reactor or parallel flow type reactor are mainly made from powder of oxidized titanium. The sintered product which is used as a catalyst or adsorbing agent is required to have a sufficiently large specific surface area for best performance. The higher the calcining temperature is, the higher the strength of the catalyst or adsorbing agent, but the specific surface area becomes smaller, which gives rise to inferior performance. In order to improve the performance the calcining temperature is made lower, but this method results in decreasing not only the adhesive force of the catalyst of adsorbing agent against a base but also the mechanical strength. Further, in order to make a honeycomb type structure through a wet type method by using the oxidized titanium powder, this method requires a large amount of water to mix and knead the oxidized titanium powder to make a viscous material, which means not only a long time is required to remove the water contained, but also the mechanical strength becomes lower. If a large amount of water is used to shape an article or structure, a porous catalyst or adsorbing agent is completed when the water is removed, so that the adhesive force and the mechanical strength becomes lower.
Regarding the titanium system catalyst it has been proposed as described in U.S. Pat. No. 4,085,193 to Nakajima et al, to use a catalyst production method of making a mixture of titanium and molybdenum, molding the mixture in tablets and calcining the molded tablets in a muffle furnace at a temperature of 500.degree. C. for four hours. The product is used for removing NO.sub.x from exhaust combustion gas. However, the patent does not disclose how to heighten the adhesive force as well as the mechanical strength of the catalyst or adsorbing agent.